TISP1072F3, TISP1082F3
DUAL ASYMMETRICAL TRANSIENT
VOLTAGE SUPPRESSORS
SEPTEMBER 1993 - REVISED SEPTEMBER 1997
APPLICATIONS INFORMATION
electrical characteristics
The electrical characteristics of a TISP are strongly dependent on junction temperature, T . Hence a
J
characteristic value will depend on the junction temperature at the instant of measurement. The values given
in this data sheet were measured on commercial testers, which generally minimise the temperature rise
caused by testing. Application values may be calculated from the parameters’ temperature coefficient, the
power dissipated and the thermal response curve ,Z (see M. J. Maytum, "Transient Suppressor Dynamic
q
Parameters."TI Technical Journal, vol. 6, No. 4, pp.63-70, July-August 1989).
lightning surge
wave shape notation
Most lightning tests, used for equipment verification, specify a unidirectional sawtooth waveform which has an
exponential rise and an exponential decay. Wave shapes are classified in terms of peak amplitude (voltage
or current), rise time and a decay time to 50% of the maximum amplitude. The notation used for the wave
shape is amplitude, rise time/decay time. A 50A, 5/310 µs wave shape would have a peak current value of
50 A, a rise time of 5 µs and a decay time of 310 µs. The TISP surge current graph comprehends the wave
shapes of commonly used surges.
generators
There are three categories of surge generator type, single wave shape, combination wave shape and circuit
defined. Single wave shape generators have essentially the same wave shape for the open circuit voltage
and short circuit current (e.g. 10/1000 µs open circuit voltage and short circuit current). Combination
generators have two wave shapes, one for the open circuit voltage and the other for the short circuit current
(e.g. 1.2/50 µs open circuit voltage and 8/20 µs short circuit current) Circuit specified generators usually
equate to a combination generator, although typically only the open circuit voltage waveshape is referenced
(e.g. a 10/700 µs open circuit voltage generator typically produces a 5/310 µs short circuit current). If the
combination or circuit defined generators operate into a finite resistance the wave shape produced is
intermediate between the open circuit and short circuit values.
current rating
When the TISP switches into the on-state it has a very low impedance. As a result, although the surge wave
shape may be defined in terms of open circuit voltage, it is the current wave shape that must be used to
assess the required TISP surge capability. As an example, the CCITT IX K17 1.5 kV, 10/700 µs surge is
changed to a 38 A, 5/310 µs waveshape when driving into a short circuit. Thus the TISP surge current
capability, when directly connected to the generator, will be found for the CCITT IX K17 waveform at 310 µs
on the surge graph and not 700 µs. Some common short circuit equivalents are tabulated below:
STANDARD
OPEN CIRCUIT
VOLTAGE
SHORT CIRCUIT
CURRENT
CCITT IX K17
CCITT IX K20
RLM88
VDE 0433
FTZ R12
1.5 kV, 10/700 µs
1 kV, 10/700 µs
1.5 kV, 0.5/700 µs
2.0 kV, 10/700 µs
2.0 kV, 10/700 µs
38 A, 5/310 µs
25 A, 5/310 µs
38 A, 0.2/310 µs
50 A, 5/200 µs
50 A, 5/310 µs
Any series resistance in the protected equipment will reduce the peak circuit current to less than the
generators’ short circuit value. A 2 kV open circuit voltage, 50 A short circuit current generator has an
effective output impedance of 40 W (2000/50). If the equipment has a series resistance of 25 W then the
surge current requirement of the TISP becomes 31 A (2000/65) and not 50 A.
P R O D U C T
I N F O R M A T I O N
10
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